• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

engaging and disengaging the overdrive

Share this page

L

Leibinger

Freshman Member
Offline
Hi all,
This might sound like a stupid question, but there are no stupid questions, especially in a forum - right?

I have been wondering and gotten lots of advise on how to engage and disengage the overdrive correctly. Originally, I thought that switchin it on or off and then getting it to engage by going off the accelerator for a moment was correct, due to the overdrive itself being a clutch an the planetary gears always being engaged.
Lately I was told that it would be better to press the clutch, then to switch it on or off and then to let go of the clutch.
Which is correct?
 
The Type A OD as found in the "Big Healeys" is a very sturdy unit. It won't hurt anything to engage OD with the throttle on. If the control circuits are adjusted correctly, it won't down shift (disengage) unless a bit of throttle is applied. All of the suggested clutch operations don't accomplish much, if anything. I guess, do whatever makes you the most comfortable.
D
 
HI Leibinger, what we call the "Bang Bang" overdrives used in the small early Volvo cars do not contain an accumulator and to prevent shock to the tranny gears the clutch must be used. OTOH, the Healey OVD does not require use of the clutch. Like Dave said do it that way if you like.---Keoke
 
Hi Peter, It has been my experience and I have read and been told that the O/D should not be shifted either up or down while the engine is in the decellerateing mode. That is why the controls (significately the throttle switch) are intended to be adjusted so that the O/D won't shift until you have the pedal about 1/5th of the way depressed. That way there is alittle power on when it shifts. If you shift the o/d when the engine is in a decellerating mode it is going to make the rear wheels try to change their road speed so drastically because of the change of gear ratio, that is has no option but to force a sever jolt to the whole drive line. The weakest part will eventually give way. You can shift with the use of the clutch with the clutch pedal depressed because then there is not load on the driveline at that time and then releasing the clutch to easy the transition to the loweer gear ratio. but this is like engine braking to come to a slower speed and is not usually done every time one slows down. Obviously you can shift into o/d on hard excelleration without the clutch because that is what was done when racing and we all know Healeys have been raced. Probably the best course of action is to adjust all the controls and switches related to the o/d as per the manual and let the machine do it's thing. A recommendation I must confess that I am not following because I have been switching the o/d with just the dash switch for about 3 years now. But I am always careful not to switch it when the engine is decellerating. When I'm slowing for an off ramp or something like that, I just lay on the gas pedal just a wee bit and shift it down.

/ubbthreads/images/graemlins/cheers.gif
 
Back
Top